New research reveals that even small amounts of one chemical found in sunscreen can have a big effect on developing corals. Oxybenzone kills polyps by deforming their cells, damaging their DNA and triggering the release of hormones that cause the young corals to encase themselves in skeleton. Mother Jones reports that just one drop of oxybenzone in a volume of water equivalent to 6.5 Olympic swimming pools can be harmful to corals.

The researchers, whose findings are published in the Archives of Environmental Contamination and Toxicology, collected coral samples from off the shores of Hawaii, the U.S. Virgin Islands and Israel. They examined seven species of corals in total.

The researchers say sunscreens that use mineral blockers are a safe choice for corals. They’re also likely a safer choice for people. According to the Environmental Working Group, this is an ingredient to watch out for, because it's associated with hormone disruption and allergic skin reactions in some people.

The need to understand the threats facing coral reefs is urgent, as coral bleaching events are becoming a more frequent occurrence. Right now, a massive bleaching event is underway in waters off Hawaii. There are a number of factors that contribute to bleaching, including warmer waters and other toxins.

Corals serve a number of important functions. They are key to ocean ecosystems, and help support millions of other marine species. They also support the communities that rely on fishing for food and income. Corals help protect people on the land by breaking up violent waves before they hit shore. According to one analysis published last year, nearly 200 million people around the world benefit from the protection of coral reefs during severe weather.

So, the next time you shop for sunscreen, be sure to skip products with oxybenzone on the ingredients list.